Traditional dry eye solutions, i.e., those for topical instillation of lubricating and wetting eye drops, contain tear substitutes. Tear substitutes or “artificial tears” attempt to emulate the composition and pH of normal tears and are intended to improve the continuous film and wetting over the corneal epithelial layer. For efficacy, the solutions often times may require instillation ten (10) times in a sixteen (16) hour day.
Traditional dry eye solutions consist of an isotonic or hypotonic aqueous solution of crystalloids, usually electrolytes of low molecular weight, carbohydrates and synthetic polymers, as well as preservatives. Synthetic polymers were generally added to dry eye solutions to increase the viscosity and retention time of the solution on the surface of the eye. However, increased viscosity interferes with lubrication. Further, an excess amount of the synthetic polymer decreases vision acuity. Many dry eye solutions also contain a preservative with bacteriostatic or bacteriocidal properties to extend the shelf life of the solution. Unfortunately, the preservative often causes allergic reactions, some of which are severe. To address this problem, some artificial tears are packaged singly and without a preservative. Nevertheless, allergic reactions may also be caused by other molecules in the solution, e.g., by pathogens or other immunogenic molecules in the solvent for dry eye solutions, i.e., water. Moreover, some traditional dry eye solutions combine indiscriminately cations and anions as well as non-ionic agents, which renders the resulting solutions electrostatically incompatible. See, e.g., U.S. Pat. No. 4,371,522; U.S. Pat. No. 4,775,531; U.S. Pat. No. 4,914,088, Glonet et al., 1995; JP Application 784147 and U.S. Pat. No. 6,428,453.
Thus, what is needed is an improved composition to treat dry eyes.